Aim: Sigma measurements are a standard tool for quality assessment of test performance in a laboratory. In this study, we aimed to calculate sigma metrics and quality goal index (QGI) for 28 biochemical parameters. Sigma values of each assay were calculated, based on the bias and coefficient of variation from internal quality control (IQC) and external quality assurance scheme (EQAS).

Material and Methods: External quality assessment (EQA) and internal quality control data for 28 parameters in a biochemical laboratory were collected from July 2019 to February 2020. The sigma values of each assay were calculated, based on the bias, total error allowable, and coefficient of variation, according to the quality goal index, the main causes of poor performance were determined to guide quality improvement. This study was conducted in the Haseki Training and Research Hospital Biochemistry Laboratory. Sigma metrics calculation was performed as (TEA − Bias)/CV for 28 biochemistry parameters analyzed with AU5800 [Beckman Coulter (BC), USA]. Total allowable errors were followed as per Clinical Laboratory Improvement Amendments (CLIA) guidelines.

Results: At IQC 1, eight of the 28 parameters (AST, ALT, LDH, CK, ALP, HDL, T. Bil

and D. Bil) showed world-class performance. At IQC 2, three of the 28 parameters (ALP, T.bil, and Crea) achieved 6 sigma (world-class performance), and three parameters (Amilase, K, Cl, and Lipase) showed world-class performance for EQC. The quality goal index (QGI) was calculated for items with analysis performance < 3 sigma, and the main causes of poor performance were determined to guide quality improvement.

Discussion: Sigma metric analysis provides a benchmark for the laboratory to design a protocol for IQC, address poor assay performance, and assess the efficiency of the existing laboratory process. Six Sigma methodology is an effective tool for evaluating the performance of biochemical analytes and conducive to quality assurance and improvement. The quality goal index is a calculation that complements this method.